1. Field of the Invention
The present invention relates to a control device applicable to a touch panel.
2. Description of the Related Art
Touch panels are widely applied in a variety of fields such as home appliances, communication devices and electronic information devices. The touch panel is often applied in input interfaces of personal digital to assistants (PDAs), electronic products and game consoles. The current trend of integrating a touch panel and a display allows a user to select an icon displayed on the panel by using a finger or a touch pen, so that the PDA, the electric product, or the game console executes a desired function. The touch panel may also be applied in a public information inquiry system, so that the user can operate the system more efficiently.
In order to effectively detect a correct position at which the user touches the panel, multiple technologies of the touch panel have been developed. For example, the touch panel may be designed as a capacitive touch panel, which is based on the positioning principle of judging a touch position according to a change of capacitance of a sensing grid embedded in the touch panel. In addition to the capacitive touch panel, other touch panels based on different sensing principles include resistive touch panels, optical touch panels and surface acoustic wave touch screen panels.
FIG. 1 is a schematic view of a conventional touch panel 10. The touch panel 10 includes a plurality of X-directional sensing lines X1 to Xm, and a plurality of Y-directional sensing lines Y1 to Yn, where m and n are same or different positive integers. The X-directional sensing lines X1 to Xm and the Y-directional sensing lines Y1 to Yn are embedded in different layers of the touch panel 10. Referring to FIG. 1, the X-directional sensing lines X1 to Xm and the Y-directional sensing lines Y1 to Yn are arranged in a staggered manner, thereby forming a sensing grid. In the sensing grid, a plurality of mutual capacitors (not shown) are formed between every X-directional sensing line and every Y-directional sensing line, and a number of parasitic capacitors (not shown) are formed between every X-directional sensing line and the ground.
During operation, a drive signal (usually a square-wave signal) is input to the X-directional sensing lines or the Y-directional sensing lines. As a result of a coupling effect of the mutual capacitors, a plurality of induced voltages are generated on corresponding Y-directional sensing lines or X-directional sensing lines. As values of the induced voltages change while a user touches the sensing lines, a position touched by the user can be acquired by detecting differences between the induced voltages.
However, due to the resistance of the sensing lines and the parasitic capacitors in the touch panel, the induced voltages can only become stable and measurable after a time delay. The time delay severely affects an operating frequency of the drive signal and a detection time of the induced voltages, and the problem becomes more serious as the size of the touch panel increases. Therefore, it is necessary to provide a control device applicable to a touch panel to meet requirements of the industry.